Polyurethane polymers, that is, polymers prepared from compounds with an active hydrogen-containing functionality, such as for example, an amine or a polyol, with a isocyanate, either a polyisocyanate or a prepolymer, are widely employed in a number of processes. In particular, polyurethanes are employed in cast-type molding processes and more particularly in RIM processes. Thermosetting urethane polymer compositions particularly useful in the RIM processes typically comprise isocyanates, such as an isocyanate (MDI-polyol) prepolymer with excess isocyanate and an aromatic diamine as a chain extender, and more particularly an alkyl aromatic diamine for reaction with the isocyanate to form a polyurea-type urethane polymer. Optionally, the polymer composition may also contain additional reactive amounts of a polyol to form a hybrid urea urethane polymer, and optionally such compositions may include a catalytic amount of a catalyst, such as an organo-metallic catalyst and an amine or a combination.
Polyurethane compositions are widely used in the preparation of molded articles, particularly by the RIM process and wherein polyurethanes are employed with a chain extender mixture as a curing agent for forming molded articles having a high flexual modulus.
One widely used chain extender are di-alkyl aromatic diamines, and more particularly, di-ethyl toluene diamine and similar aromatic diamines for use with isocyanate prepolymers alone or with a polyol to form a hybrid polyurea polyurethane molding RIM composition. The chain extender known as DETDA is commercially used and comprises a mixture of isomers having about 76% of 1 methyl 3,5 di-ethyl 2,4 diamino benzene and about 24% of 1 methyl 3,5 di-ethyl 2,6 diamino benzene, that is, a ratio of about 80:20. DETDA is used as a chain extender with polyisocyanates and provides molded articles of the desired physical properties employed in the molding of automotive type articles, but its use is not restricted to such articles. The employment of di-alkyl aromatic diamine as chain extenders is set forth in U.S. Pat. No. 4,218,543, issued Aug. 19, 1980, hereby incorporated by reference. One problem associated with the use of DETDA compositions in RIM processes is that the gel time is quite short, for example, typically less than two seconds when employed with isocyanate prepolymers, such as MDI prepolymers. The molded article typically does not have a flexual modulus above about 80,000 psi at 75.degree. F. without exhibiting an undesirable property known as "cold break" after demolding.
Other polyurethane chain extenders have been developed, such as for example, the di-alkyl thiodiamine chain extenders, and more typically, a mixture of the 2,4 and 2,6 isomers of the dimethyl thiotoluene diamine as described in U.S. Pat. No. 4,595,742, issued June 17, 1986, and sold commercially as ETHACURE-300 (a trademark of the Ethyl Corporation). The thiodiamine chain extenders do not have the rapid gel times of the DETDA compositions in RIM compositions, but rather extended gel times usually over 15 seconds. In addition, due to the thio linkage, the thio chain extenders are often undesirable and may create a sulfur or thio smell in the molded article. The thio chain extenders, like the DETDA, also do not provide for molded RIM articles in a RIM process with a flexual modulus above 80,000-90,000 psi without "cold break" in the molded article.
In an attempt to modify and control the difference in the gel times in the chain extenders, the chain extenders have been mixed to form a mixture of a di-alkyl toluene diamine and di-alkyl thiotoluene diamine, such as for example, as described in the U.S. Pat. No. 4,631,298, issued Dec. 23, 1986, hereby incorporated by reference. Further, polyhydroxy alkyl aromatic diamine compounds have been developed as chain extenders particularly for use in a RIM process with MDI prepolymers and wherein the chain extender composition comprises a blend of a polyol, like 1,4 butane diol and the di-alkyl thiotoluene diamine, which is described in U.S. Pat. No. 4,786,656, issued Nov. 22, 1988, hereby incorporated by reference.
It is desirable to provide for new and improved polyurethane compositions, particularly suitable for use in a RIM process, and more particularly, polyurea or hybrid polyurea polyurethane molding compositions to provide for an article having high, flexual strength and a practical, workable gel time and yet without exhibiting "cold break" properties on demolding.